Maybe America should have seen it coming. The Colonel is just the latest fast food mascot to enjoy a revival.

McDonald’s has brought back the Hamburglar. Burger King has returned the King. It’s not just fast food: characters like the Maytag Man and 9Lives’s Morris the Cat have also recently found new life, as brands try to give their old characters a facelift that will resonate with younger consumers.

“Mascots can work tremendously well online on social media for corporate brands and product brands,” said branding consultant Dean Crutchfield. “The key I think about mascots is that they cut through the clutter.”

To be sure, nostalgia is a tried-and-true marketing technique. In recent years, as marketers gravitated toward social media, what is old has become new again. Characters from the Aflac duck to P&G’s Mr. Clean have taken center stage through tweets and Facebook posts.

For KFC, the return of the Colonel was in part about restoring consumers’ trust in the quality of the chicken, according to Kevin Hochman, chief marketing officer at KFC U.S. The original Colonel Sanders, who created the company and died in 1980, represented that KFC wasn’t “cutting corners,” according to Mr. Hochman.

KFC wanted to bring back the showmanship of a funny and “over-the-top chicken salesman,” which Mr. Hochman says will connect with a knowing younger generation keenly aware of when they are being pitched by an advertiser. The revival also commemorates KFC’s 75th anniversary.

But weeks before KFC’s move, McDonald’s made a splash when it brought back the Hamburglar. Some on social media liked the sexified mascot, but others thought the stubble-faced hipster thief looked “creepy.”

Mascots are often widely familiar among U.S. consumers. According to the Q Scores Company, 93% of consumers are familiar with the King, while 84% know the Hamburglar and 81% know the Colonel. But whether or not consumers actually like mascots can vary: 42% of those familiar with the King reacted negatively to the character, while 29% and 32% of consumers reacted negatively toward the Hamburglar and Colonel, respectively. It’s unclear whether general resistance to fast food impacted the scores.

There may be another reason brands rely on old stars: they’re cheaper.

Given the fractured media environment, “Creating a new mascot is almost a mountain that’s too high to climb,” said Allen Adamson, chairman of Landor North America, a WPP-owned branding firm.

Mr. Adamson estimates that fewer than 25% of brands use a mascot. But dusting one off means a company has to make the mascot feel young and contemporary.

“Millennials are very interested in the authenticity and the history of the brands they interact with. One way to bring that authentic story back to life is to take an icon or an old mascot and bring it back,” Mr. Adamson said.

For its part, KFC wasn’t expecting its Colonel campaign to be a part of some larger advertising trend.

“We had no idea that some of these other mascots would be coming back,” Mr. Hochman said.